Brushless direct current motor

ABSTRACT

In brushless direct current motors having pairs of axially spaced permanent magnets radially arranged about and fixed to a rotor shaft, driving coils disposed in the space between said pairs of permanent magnets and detecting means including detecting coils, and a shield ring having cutaway portions in the path of said detecting coil for the operation of each detecting coil when said cutaway portions are aligned therewith for the activation of the driving coil associated with said detecting coil; the improvement of mounting the driving coils in apertures in an insulated board at an angular interval of about 100* and forming said board with a notch extending from the edge thereof to the center of said driving coils to permit removal of said rotor shaft.

United States Patent [72] Inventor lssei lmahashi 3,290,572 12/1966l-lartmann 318/138 Suwa-shi, Japan 3,317,803 5/1967 1kegami......318/138 [21] Appl. No. 820,200 3,364,407 1/1968 Hill 318/138 [22] FiledApr. 29, 1969 3,402,333 9/1968 Hayner 310/49 [45] Patented May l8,1 9713,453,512 7/1969 Polakowski 318/ 138 173 l i f Primary ExaminerMilton 0.l-lirshfield [32] Priority Apr. 30, 1968 As t E R Sk d [33] Java Att ani t f 1 d & K 1 n [3 ts/28687 0rney um, oscovi rte man ap a {54]BRUSHLESS DIRECT CURRENT MOTOR ABSTRACT: In brushless direct currentmotors having pairs of axially spaced permanent magnets radiallyarranged about 5 Clalms, 6 Drawing Figs.

and fixed to a rotor shaft, dnvmg coils disposed 111 the space [52] U.S.Cl 310/ 156, between aid airs of permanent magnets and detecting means 30/ including detecting coils, and a shield ring having cutaway E t g l ol POI'EOSS in the patlli ofhsaid deecting coil for the operation 0;

eac etectmg cm W en sai cutaway portions are a igne 63 therewith for theactivation of the driving coil associated with 171, 474 said detectingcoil; the improvement of mounting the driving 56 R f coils in aperturesin an insulated board at an angular interval 1 SgXE SZf of about 100 andforming said board with a notch extending from the edge thereof to thecenter of said driving coils to permit removal of said rotor shaft.

Patented May 18, 1971 3,579,277

4 SheetsSheet l F/GJ Patented May 18, 1971 4 Sheets-Sheet 2 Patent edMay 18, 1971 I 3,579,271

.4 Sheets-Sheet 3 Patented Ma 18, 1971 3,579,277 I 4 sheets-sheet 4BACKGROUND OF THE INVENTION This invention relates generally tobrushless direct current motors adapted for operation in connection withtransistorized driving circuits. Many forms of such direct currentmotors have been proposed but they all suffer from the disadvantages ofnot being self-starting and of failing to consistently rotate the motorthereof in a predetermined direction. One proposed approach to overcomethese difficul ties is the provision of a hall effect sensing elementbut the cost of such elements is extremely high. By providing a properalignment of driving coils and detecting arrangement as taught in thecopending application of Chifumi Komatsu for Brushless Direct CurrentMotor," assigned to the assignee herein, the foregoing defects have beenavoided while provid ing a brushless direct current motor of relativelylow cost. Still further efficiencies in compactness and economy can beachieved by the proper mounting of the elements as taught herein.

Generally speaking, a brushless direct current motor may be providedwhich includes pairs of axially spaced permanent magnets radiallyarranged about and fixed relative toa rotor shaft. Driving coils aredisposed in the space between said pairs of permanent magnets and adetecting means having detecting coils is also provided. At least onedetecting coil is provided for each driving coil, the number thereofpreferably equaling one-half of the number of pairs of permanent magnetsprovided. The driving coils are radially arranged about said rotor shaftso that, at any position of said permanent magnets, at least one of saiddriving coils is positioned with each of two sides thereof within thegap between different pairs of permanent magnets, said different pairsof permanent magnets being aligned to produce a force on said rotorshaft in the same direction. Further, said detecting means is disposedso that the detecting coils associated with at least one of the drivingcoils aligned to produce a force on said rotor shaft is activated.

The detecting means preferably includes a plurality of pairs of axiallyspaced detecting coils spaced about said rotor shaft and a conductingshield plate mounted for rotation with said rotor shaft and extendinginto the space between said detecting coils, said shield plate beingformed with portions cut away to permit activation, at any position ofsaid shield plate of at least the detecting coil associated with atleast one of the driving coils aligned to produce a driving force atthat position.

In the improvement in accordance with the invention, the driving coilsare supported in apertures formed in a planar base made of insulatingmaterial. The coils are disposed on the base at an angular interval ofabout 100 about said rotor shaft. The base is provided with a notchextending from one edge thereof to the center of the three coils, saidnotch being adapted to receive said rotor shaft and to permit theinsertion and removal thereof. Further, the detecting coils are disposedat an angular interval of 40 degrees about said rotor shaft.

Accordingly, it is an object of this invention to provide a brushlessdirect current motor which can be readily assembled and disassembled. II

Another object of the invention is to provide a brushless direct currentmotor which is self starting, always rotates in .the predetermineddirection, and is of extremely simple construction and relatively lowcost.

Still other objects and advantages of the invention will in part beobvious and will in part be apparent from the specification.

The invention accordingly comprises the features of con- BRIEFDESCRIPTION OF THE DRAWINGS For a fuller understanding ofthe invention,reference is had to the following description taken in connection withthe accompanying drawings, in which:

FIG. 1 is an exploded perspective view of a brushless direct currentmotor according to the invention;

FIG. 2 shows an enlarged exploded view of the driving coils andpermanent magnets of the motor of FIG. 1;

FIG. 3 is a top plan view of the shield plate of the motor of FIG. 1;

FIG. 4 is a top plan view of the detecting coils of the motor accordingto FIG. 1;

FIG. 5 is a block diagram showing the driving circuit for the motor ofFIG. I; and

FIG. 6 is a perspective view of the assembled brushless direct currentmotor of FIG. 1 with portions broken away.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. I, thedirect current brushless motor shown is exploded along the axis of rotorshaft 1 thereof away from yoke 2. When assembled as shown in FIG. 6,yokes 2 and 3 are mounted on shaft 1 in spaced relation. Arrangedradially about shaft I are pairs of permanent magnets 4 and 10, 5 and11,6 and 12, 7 and i3, 8 and 14, and 9. and 15. One ofeach of said pairsof permanent magnets, namely magnets 4, 5, 6, 7, 8 and 9, are fixedlysecured to yoke 2, while the other of said permanent magnets are fixedlysecured to yoke 3. Each of said permanent magnets is sector shaped,defining a sector of an arc about shaft 1. Each of said pairs ofpermanent magnets are in spaced relation and disposed with oppositepoles in facing relation. Thus, the south pole of magnet 7 faces thenorth pole of magnet 13. Further, the six poles secured to each yoke anddisposed so that adjacent magnets have their opposite poles facing theairgap between said pairs of permanent magnets to produce a magneticfield in said gap. Thus, permanent magnet 4 has its north pole facingthe airgap and its companion permanent magnet 10, while the adjacentpermanent magnets 9 and 5 both have their south poles facing said airgapand their respective companion magnets. By this arrangement, themagnetic fields between pairs 4 and 10, 6 and 12 and 8 and 14 extend inthe direction of arrow 50 while the fields between pairs 5 and 11, 7 and13 and 9 and 15 extend in the direction of arrow 51.

Disposed in the airgap between said pairs of permanent magnets aresubstantially trapezoidal flat driving coils 17, 18 and 19. Said drivingcoils are radially arranged about rotor shaft 1 but are mountedindependently thereof in apertures in a base 52 of insulating materialas more particularly shown in FIGS. 2 and 6. The permanent magnets arecircumferentially distributed about shaft 1 at equal intervals of 60degrees. The three driving coils 17, 18 and 19 are mounted on base 52 ata circumferential interval of about said shaft. Further, said drivingcoils are arranged so that the angles defined between the centerlines ofsides 38 and 39 of coil 17, sides 41 and 42 of coil 18 and sides 44 and45 of coil 19 all equal 60. Also as shown in FIG. 2, base 52 is providedwith a notch 53 extending from one edge thereof to the center of saiddriving coils, said notch being adapted to accommodate rotor shaft 1during normal operation and for the insertion and removal thereof. Alsomounted on base 52 are electronic circuit elements 100 such astransistors, resistors and capacitors defining the circuitry associatedwith the driving coils.

Also provided is a detecting means consisting of three pairs ofdetecting coils 25 and 26, 27 and 28, and 29 and 30, as moreparticularly shown in FIG. 4. Said detecting coils are preferably formedin the shape of small discs with the detecting coils forming each pairbeing disposed in spaced relation with an airgap therebetween. Saidpairs of detecting coils are disposed radially about rotor shaft 1 withan angle of 40 being defined between pairs 25 (26) and 27 (28), and 29(30), respectively. As shown in FIG. 6, detecting coils 26, 28 and 30are mounted on circuit board 101 while detecting coils 25, 27

and 29, not Sh wn n H 6. a mOllnIed Circuit board However, it has beenfound that by disposing the coils at an 101. Circuit boards 101 and 101'are mounted in spaced relai t v l f l00, a device which is readilyassembled and tion to each other an to b 52 y spacers 102 moun e onmanufactured is produced. This results from the fact that the bolts 103.Said detecting means also includes a shield plate 31 d i i g il are nott k d o e upon another and that notch as shown in FIG. 3 fixedly mountedto rotor shaft 1 and ex- 53 oan b ided in ba e 52 to permit theinsertion and tending into the gap between said pairs of detectingcoils. The removal f rotor h f 1 Th latter b di hi h i i shield plate isformed with three cutaway regions 32 Within the tured in the drawingshas driving coil 18 disposed at 100 relapath of said detector coilairgaps. Said cutaway regions are ti t d i i il 17, and d i i oil 19disposed at 200 spaced equally radially about rotor shaft 1, each of Sairelative to driving coil 17, thereby producing the 100 interval openingsdefining a 40 sector. Shield plate 31 is preferably 0 betweencorresponding radial edges of adjacent driving coils.

formed from a material of low electric resistance, such as alu- Inaddition, there are a variety of arrangements'for the deminum. tectingcoils according to the invention but, by disposing said R r ng H to lthe driving circuits of motor detecting coils at an interval of 40 onone side of the device, a

according to the invention as shown. Each driving circuit coni l u tiarrangement may be provided as shown in sists of a oscillator 68, 69 and70, a demodulating circuit 71, FIG, 6,

72and 73 forrectifying the output of the oscillators and a By arrangingthe motor according to the invention in the power amplifier 74, 75 and76 for applying a driving current to preferred manner, a motor isproduced which is inexpensive to the corresponding driving coils. One ofthe pairs of detecting produce and operate while being extremelycompact.

coils is connected to each oscillator circuit to govern the oscil- Itwill thus be seen that the objects set forth above, among lation thereofwhile a corresponding driving coil is connected 20 those made apparentfrom the preceding description, are effito the Output of the poweramplifiersciently attained and, since certain changes may be made in theReferring now to FIGS. l4, the operation of the motor acaboveconstructions without departing from the spirit and cording to theinvention is explained as follows. When the cuscope of the invention, itis intended that all matter contained taway portion of 32 shield plate31 positioned opposite detecting coils 27 (28), the oscillator 69connected to this coil comin the above description or shown in theaccompanying drawings shall be interpreted as illustrative and not in alimitmences oscillation. The oscillating wave is demodulated by ingsense. demodulator 72, amplified by power amplifier 75 to apply lclaim:driving current through driving coil 18. When the current 1. In a directcurrent brushless motor having a rotor shaft, a flows through saiddriving coil in the direction of arrows 60 pair of spaced yokes mountedon said shaft for rotation and 61, the side 41 of said driving coil actson the pair of pertherewith, a plurality of pairs of permanent magnetsradially manent magnets 5 and 11, while the side 42 thereof acts onarranged about said shaft between said yokes, one of each of the pair ofpennanent magnets 6 and 12, to produce a force in said pairs ofpermanent magnets being mounted on each of the direction of arrow 57 inaccordance with the normal laws said yokes with a gap therebetween, aplurality of driving coils of magnetic fields. Accordingly, the wholerotor assembly indisposed in the gap between said pairs of permanentmagnets, cluding shield disc 31 rotates in the direction of said arrow57. and a detecting means responsive to the position of said rotor yVhenrotor shaft 1 has rotated about in the direction of shaft and having atleast one detecting coil associated with arrow Shield plate 31 isinterposed between the pair of deeach driving coil for the activation ofsaid driving coil to rotate tecting coils 27 and 28 to stop theoscillation of oscillator 69. aid rotor shaft, the improvement whichcomprises providing During the above-described P Shield Plate 31 W88inter- 40 three nonoverlapping driving coils having correspondingradiposed between the other pairs of detecting coils to prevent the aledges thereof circumferentially spaced-about said shaft at oscillationof oscillator 68 and 70. However, at the moment an angular interval ofabout l00, said motor including a base h oscillator 69 stops operation,Cutaway r gion 32 i having said three driving coils mounted thereon,said base disposed opposite detecting coils 29 (30) causing oscillator68 being formed with a notch extending from one edge thereof to tocommence operation to apply driving current to coil 19. 45 the center ofsaid driving coils, said notch being adapted to When the curr nt flowsthrough driving il 19 n th receive said motor shaft during the operationof said motor direction of arrows 58 and 59, the side 45 of said drivingcoil and to permit the displacement of said rotor shaft therealong. actson the pair of permanent magnets 7 and 13 while the side 2. A directcurrent brushless motor as recited in claim 1, 44 acts on the pair ofpermanent magnets 6 and 12 to apply a wherein said detecting meansincludes a shield ring on said force to the rotor assembly to continuethe rotation thereof in shaft formed from a conducting material andhaving cutaway the direction of arrow 57. Of course, the rotation ofshaft 1 portions in the path of said detecting coils to permit theoperacarries with it yokes 2 and 3, the permanent magnets, and tion ofeach of said detecting coils when said cutaway portions shield disc 31.This portion of the cycle continues while the are aligned therewith forthe activation of the associated drivrotor rotates 40 until shield plate31 is interposed between ing coil to rotate said rotor shaft. detectingcoils 29 (30) while cutaway region 32 is disposed 3. A brushless directcurrent motor as recited in claim 2, opposite detecting coils 25 (26)'toapply a driving current to wherein the poles ofeach pair of permanentmagnets defining driving coil 17. When the current flows through coil 17in the the gap therebetween are of opposite polarity to produce adirection of arrows 62 and 63, the side 39 of said coil acts on magnetifield in said gap and the poles of adjacent permanent the pair ofpermanent magnets 8 and 14, while the side 38 acts magnets on each ofsaid yokes are of different polarity, said on the pair of permanentmagnets 9 and 14 to produce a conmotor being provided with six pairs ofpermanent magnets cirtinued rotative force in the-direction of arrow 57.cumferentially spaced about said rotor so that each of said Theabove-described cycle is repeated with every 120 rotapairs of permanentmagnets substantially occupies a 60 section of the rotor shaft with thedetecting coils and driving coils tor, each of said driving coilssubstantially occupying a 60 being sequentially activated tocontinuously rotate the rotor sector. shaft in apredetermined direction.65 4. A direct current brushless motor as recited in claim 2, Drivingcoils 17, 18 and 19 may be disposed in a variety of wherein said shieldring has a plurality of cutaway portions in positions. Thus, thefollowing chart represents some examples the path of said detectingcoils each permitting the operation of the angular displacement at whichdriving coils 18 and 19 of a detecting coil when said cutaway portion isaligned may be disposed relative to driving coils 17. therewith for theactivation of the driving coil associated with said detecting coil, saiddetecting coils being spaced circumferentially about the rotor shaft at40 intervals, each of said 18 cutaway portions defining a 40circumferential are about said 40 degrees. 20 degrees. rotor shaft.

%% 32553:? ig ggggz- 5. A direct current brushless motor as recited inclaim 4, 220 degrees: 200 degrees: wherein saidmotor is provided withthree sets of detecting :28 3253:: 22% 32322:: coils, said shield rmgbeing provided with three cutaway regions eouallv spaced about saidrotor shaft.

1. In a direct current brushless motor having a rotor shaft, a pair ofspaced yokes mounted on said shaft for rotation therewith, a pluralityof pairs of permanent magnets radially arranged about said shaft betweensaid yokes, one of each of said pairs of permanent magnets being mountedon each of said yokes with a gap therebetween, a plurality of drivingcoils disposed in the gap between said pairs of permanent magnets, and adetecting means responsive to the position of said rotor shaft andhaving at least one detecting coil associated with each driving coil forthe activation of said driving coil to rotate said rotor shaft, theimprovement which comprises providing three nonoverlapping driving coilshaving corresponding radial edges thereof circumferentially spaced aboutsaid shaft at an angular interval of about 100*, said motor including abase havinG said three driving coils mounted thereon, said base beingformed with a notch extending from one edge thereof to the center ofsaid driving coils, said notch being adapted to receive said motor shaftduring the operation of said motor and to permit the displacement ofsaid rotor shaft therealong.
 2. A direct current brushless motor asrecited in claim 1, wherein said detecting means includes a shield ringon said shaft formed from a conducting material and having cutawayportions in the path of said detecting coils to permit the operation ofeach of said detecting coils when said cutaway portions are alignedtherewith for the activation of the associated driving coil to rotatesaid rotor shaft.
 3. A brushless direct current motor as recited inclaim 2, wherein the poles of each pair of permanent magnets definingthe gap therebetween are of opposite polarity to produce a magneticfield in said gap and the poles of adjacent permanent magnets on each ofsaid yokes are of different polarity, said motor being provided with sixpairs of permanent magnets circumferentially spaced about said rotor sothat each of said pairs of permanent magnets substantially occupies a60* sector, each of said driving coils substantially occupying a 60*sector.
 4. A direct current brushless motor as recited in claim 2,wherein said shield ring has a plurality of cutaway portions in the pathof said detecting coils each permitting the operation of a detectingcoil when said cutaway portion is aligned therewith for the activationof the driving coil associated with said detecting coil, said detectingcoils being spaced circumferentially about the rotor shaft at 40*intervals, each of said cutaway portions defining a 40* circumferentialarc about said rotor shaft.
 5. A direct current brushless motor asrecited in claim 4, wherein said motor is provided with three sets ofdetecting coils, said shield ring being provided with three cutawayregions equally spaced about said rotor shaft.